Lubricating oil compositions used to lubricate internal combustion engines contain a base oil of lubricating viscosity, or a mixture of such oils, and additives used to improve the performance characteristics of the oil. For example, additives are used to improve detergency, to reduce engine wear, to provide stability against heat and oxidation, to reduce oil consumption, to inhibit corrosion, to act as a dispersant, and to reduce friction loss. Some additives provide multiple benefits, such as dispersant-viscosity modifiers. Other additives, while improving one characteristic of the lubricating oil, have an adverse effect on other characteristics. Thus, to provide lubricating oil having optimal overall performance, it is necessary to characterize and understand all the effects of the various additives available, and carefully balance the additive content of the lubricant.
It has been proposed in many patents and articles (for example, U.S. Pat. Nos. 4,164,473; 4,176,073; 4,176,074; 4,192,757; 4,248,720; 4,201,683; 4,289,635; and 4,479,883) that oil-soluble molybdenum compounds are useful as lubricant additives. In particular, the addition of molybdenum compounds to oil, particularly molybdenum dithiocarbamate compounds, provide the oil with improved boundary friction characteristics and bench tests demonstrate that the coefficient of friction of oil containing such molybdenum compounds is generally lower than that of oil containing organic friction modifiers. This reduction in coefficient of friction results in improved antiwear properties and may contribute to enhanced fuel economy in gasoline or diesel fired engines, including both short- and long-term fuel economy properties (i.e., fuel economy retention properties). To provide antiwear effects, molybdenum compounds are generally added in amounts introducing from about 350 ppm up to 2,000 ppm of molybdenum into the oil. While molybdenum compounds are effective antiwear agents and may further provide fuel economy benefits, such molybdenum compounds are expensive relative to more conventional, metal-free (ashless) organic friction modifiers.
Despite the foregoing, there continues to be a need for more cost effective lubricant compositions that provide equivalent or superior performance to lubricant compositions without the presence of molybdenum-based friction modifiers.
In accordance with a first aspect, one exemplary embodiment of the disclosure provides an improved lubricating oil composition substantially devoid of molybdenum compounds that may provide equivalent or superior lubricating properties. The lubricating oil composition has therein at least one succinimide dispersant derived from a polyalkylene compound having from about 50 to about 85% vinylidene double bonds in the compound. A metal containing detergent, at least one wear reducing agent, at least one antioxidant, and a hydrocarbon soluble titanium compound as a friction modifier are also included in the lubricating oil. The lubricating oil composition is substantially free of molybdenum compounds.
In accordance with a second aspect, the disclosure provides a lubricant additive concentrate for reducing sludge in a lubricant composition. The concentrate is devoid of molybdenum and contains a hydrocarbyl carrier fluid, at least one succinimide dispersant derived from a polyalkylene compound having from about 50 to about 85% vinylidene double bonds in the compound. Also included in the concentrate is a hydrocarbon soluble titanium compound as a friction modifier providing from about 10 to about 500 ppm titanium to the lubricant composition.
In accordance with a third aspect, the disclosure provides a lubricated surface having a lubricant composition containing a base oil of lubricating viscosity and an additive package in contact therewith. The additive package includes at least one succinimide dispersant derived from a polyalkylene compound having from about 50 to about 85% vinylidene double bonds in the compound. Also included in the additive packages is a metal containing detergent, at least one wear reducing agent, at least one antioxidant, and a hydrocarbon soluble titanium compound as a friction modifier. The lubricant compostion in contact with the surface is substantially free of molybdenum compounds.
Yet another aspect of the disclosure provides a fully formulated lubricant composition including a base oil component of lubricating viscosity and an amount of sludge reducing lubricant additive. The lubricant additive contains at least one succinimide dispersant derived from a polyalkylene compound having from about 50 to about 85% vinylidene double bonds in the compound, a metal containing detergent, at least one wear reducing agent, at least one antioxidant, and a hydrocarbon soluble titanium compound as a friction modifier providing from about 10 to about 500 ppm titanium to the lubricant composition. The lubricant composition is also substantially free of molybdenum compounds.
Still another aspect of the disclosure provides a lubricant composition containing a base oil of lubricating viscosity and an amount of at least one hydrocarbon soluble titanium compound effective to provide improved lubricant properties selected from a reduction in surface wear greater than a surface wear of a lubricant composition devoid of the hydrocarbon soluble titanium compound, a reduction in oxidation of the lubricant composition greater than a reduction in oxidation of the lubricant composition devoid of the hydrocarbon soluble titanium compound, and a reduction in sludge formation in the lubricant composition greater than a reduction in sludge formation in the lubricant composition devoid of the hydrocarbon soluble titanium compound.
One advantage of the disclosed embodiments is a significant improvement in sludge reduction over compositions containing titanium compounds and conventional succinimide dispersants. The foregoing advantage is obtained despite the absence of molybdenum containing compounds in the lubricant composition. Other advantages may include a reduction in a coefficient of friction, a reduction in surface wear, and/or a reduction in oxidation of the lubricant composition. Other and further objects, advantages and features of the disclosed embodiments may be understood by reference to the following.